Metalloproteins (MTs) are one of the most diverse classes of proteins, with the intrinsic metal atoms providing a catalytic, regulatory and structural role crucial to protein functioning. When stored under aerobic conditions, MTs might form dimers (as well as higher oligomers) that play an essential role as mediators in oxidoreduction signalling pathways. In this work, we explore the non-oxidative dimerization process characterized by metal (Cd) bridging of MT monomers by Förster resonance energy transfer. The formation of MT dimers/oligomers was investigated by applying capillary electrophoresis and matrix-assisted laser desorption/ionization with mass spectrometric detection.